This is just my opinion, but I cant see the point to putting a scope on a shotgun for shots 20-40 yds. This is just my opinion. It seems like overkill, but is you want to go ahead I respect everyones decision.

If you want better sights take the ones off on your gun and buy some tru glo sights from Cabelas and Bass Pro. You can shoot with them basically when its dark. I can shoot in groups at 75 yds with my tru-glos on my BP gun.